The invention relates to a telescopic stick for a shortenable umbrella, the stick having at least two telescopic parts sliding one inside the other and secured against relative twisting by virtue of complementary polygonal cross sections associated one with each of the two parts, the parts being releasably lockable in mutually extended and/or retracted positions. Such a stick is hereinafter referred to as of the kind described.
Telescopic sticks with a prismatic profile of this kind, such as are known, for example, from the patent to Haupt; U.S. Pat. No. 2,165,962, and which are still used in the umbrella industry, hitherto fulfilled a purely functional purpose in the way that the telescopic parts of the telescopic stick, because of their square or hexagonal or polygonal cross-section, are, without expenditure for special refinements or parts, guided accurately in one another and secured against relative twisting, i.e. rotation, in order thereby to guarantee the necessary exact alignment of the different components of the umbrella with one another. In this way, the necessary alignment between the umbrella handle and certain release mechanisms at the bottom end of the stick, and the canopy kinematics at the top end of the stick, for opening and closing the umbrella, are controlled. Because of the wide fluctuations in tolerance of the dimensions of the raw stock material for polygonal tubes it is also known, for example, from the above-mentioned publication, and it is also current practice, to combine a polygonal tube with round tube in the telescopic stick, in which case polygonal reductions or sleeves are fitted onto the telescopic part manufactured from round tube, to complement the polygonal cross-section of the prismatic telescopic part. In any case, the fact is that the more a polygonal cross-sectional profile approximates that of a round cross-sectional profile, the more corners it has. Therefore, the security against relative twisting, and the accurate guidance, of the stick parts of a polygonal telescopic stick increases with the fewer the corners or facets, and decreases with the more the corners or facets; the general practice of the umbrella industry hitherto a has been to use, for shortenable umbrellas, only telescopic sticks having an external polygonal profile of not more than six corners or facets. Since the security against twisting, and the guidance, are furthermore also influenced by the fluctuations in tolerance of the tube material, the employment of polygonal tube having more than six corners or facets for telescopic sticks of shortenable umbrellas has proved to be impractical in the past. But on the other hand, it is desirable to avoid, in the case of a pocket umbrella, an appearance which leaves too functional an impression, and also to impart to the very conspicuous telescopic stick of such an umbrella a decoratively pleasing look of at least equal value to the functional external appearance. But a telescopic stick having just a few corners, in accordance with the usual practice, appears to be too clumsy and functional.